Effects of brain‐derived neurotrophic factor Val66Met polymorphism on hippocampal volume change in schizophrenia

A functional polymorphism of the brain‐derived neurotrophic factor (BDNF) gene (Val66Met) has been associated with the risk for schizophrenia and volume differences in the hippocampus. However, little is known about the association between progressive brain volume change in schizophrenia and BDNF genotype. The aim of this study was to investigate the relationship between hippocampal volume change in patients with schizophrenia and healthy control subjects and BDNF genotype. Two structural magnetic resonance imaging brain scans were acquired of 68 patients with schizophrenia and 83 healthy subjects with an interval of approximately 5 yrs. Hippocampal volume change was measured and related to BDNF genotype in patients and healthy controls. BDNF genotype was not associated with hippocampal volume change over time in patients or healthy controls, nor could we replicate earlier findings on smaller hippocampal volume in Met‐carriers. However, we did find a genotype‐by‐diagnosis interaction at baseline demonstrating smaller hippocampal volumes in patients homozygous for the Val‐allele relative to healthy Val‐homozygotes. In addition, irrespective of genotype, patients showed smaller hippocampal volumes compared with healthy controls at baseline. In summary, our results suggest that the BDNF Val66Met polymorphism is not associated with hippocampal volume change over time. Nevertheless, our findings may support the possibility that BDNF affects brain morphology differently in schizophrenia patients and healthy subjects. © 2009 Wiley‐Liss, Inc.     

Hippocampal epigenetic modification at the brain‐derived neurotrophic factor gene induced by an enriched environment

Environmental enrichment is an experimental paradigm that increases brain‐derived neurotrophic factor (BDNF) gene expression accompanied by neurogenesis in the hippocampus of rodents. In the present study, we investigated whether an enriched environment could cause epigenetic modification at the BDNF gene in the hippocampus of mice. Exposure to an enriched environment for 3–4 weeks caused a dramatic increase in the mRNA expression of BDNF, but not platelet‐derived growth factor A (PDGF‐A), PDGF‐B, vascular endothelial growth factor (VEGF), nerve growth factor (NGF), epidermal growth factor (EGF), or glial fibrillary acidic protein (GFAP), in the hippocampus of mice. Under these conditions, exposure to an enriched environment induced a significant increase in histone H3 lysine 4 (H3K4) trimethylation at the BDNF P3 and P6 promoters, in contrast to significant decreases in histone H3 lysine 9 (H3K9) trimethylation at the BDNF P4 promoter and histone H3 lysine 27 (H3K27) trimethylation at the BDNF P3 and P4 promoters without any changes in the expression of their associated histone methylases and demethylases in the hippocampus. The expression levels of several microRNAs in the hippocampus were not changed by an enriched environment. These results suggest that an enriched environment increases BDNF mRNA expression via sustained epigenetic modification in the mouse hippocampus. © 2010 Wiley‐Liss, Inc..     

The influence of aging on the methylation status of brain‐derived neurotrophic factor gene in blood

Objective

Brain‐derived neurotrophic factor (BDNF) is involved in the pathophysiology of psychiatric disorders in adults and elderly individuals, and as a result, the DNA methylation (DNAm) of the BDNF gene in peripheral tissues including blood has been extensively examined to develop a useful biomarker for psychiatric disorders. However, studies to date have not previously investigated the effect of age on DNAm of the BDNF gene in blood. In this context, we measured DNAm of 39 CpG units in the CpG island at the promoter of exon I of the BDNF gene.

Methods

We analyzed genomic DNA from peripheral blood of 105 health Japanese women 20 to 80 years of age to identify aging‐associated change in DNAm of the BDNF gene. In addition, we examined the relationship between total MMSE scores, numbers of stressful life events, and serum BDNF levels on DNAm of the BDNF gene. The DNAm rate at each CpG unit was measured using a MassArray^® system (Agena Bioscience), and serum BDNF levels were measured by ELISA.

Results

There was a significant correlation between DNAm and age in 13 CpGs. However, there was no significant correlation between DNAm and total MMSE scores, numbers of life events, or serum BDNF levels.

Conclusion

Despite the small number of subjects and the inclusion of only female subjects, our results suggest that DNAm of 13 CpGs of the BDNF gene may be an appropriate biomarker for aging and useful for predicting increased susceptibility to age‐related psychiatric disorders.     

Synaptic maturation of the Xenopus retinotectal system: Effects of brain‐derived neurotrophic factor on synapse ultrastructure

Synaptogenesis is a dynamic process that involves structural changes in developing axons and dendrites as synapses form and mature. The visual system of Xenopus laevis has been used as a model to study dynamic changes in axons and dendrites as synapses form in the living brain and the molecular mechanisms that control these processes. Brain‐derived neurotrophic factor (BDNF) contributes to the establishment and refinement of visual connectivity by modulating retinal ganglion cell (RGC) axon arborization and presynaptic differentiation. Here, we have analyzed the ultrastructural organization of the Xenopus retinotectal system to understand better the maturation of this synaptic circuit and the relation between synapse ultrastructure and the structural changes in connectivity that take place in response to BDNF. Expression of yellow fluorescent protein (YFP) followed by preembedding immunoelectron microscopy was used to identify RGC axons specifically in living tadpoles. Injection of recombinant BDNF was used to alter endogenous BDNF levels acutely in the optic tectum. Our studies reveal a rapid transition from a relatively immature synaptic circuit in which retinotectal synapses are formed on developing filopodial‐like processes to a circuit in which RGC axon terminals establish synapses with dendritic shafts and spines. Moreover, our studies reveal that BDNF treatment increases the number of spine synapses and docked vesicle number at YFP‐identified synaptic sites within 24 hours of treatment. These fine structural changes at retinotectal synapses are consistent with the role that BDNF plays in the functional maturation of synaptic circuits and with dynamic, rapid changes in synaptic connectivity during development. J. Comp. Neurol. 518:972–989, 2010. © 2009 Wiley‐Liss, Inc.     

Effects of moderate‐ and high‐intensity chronic exercise on brain‐derived neurotrophic factor expression in fast and slow muscles

Introduction: Brain‐derived neurotrophic factor (BDNF) protein expression is sensitive to cellular activity. In the sedentary state, BDNF expression is affected by the muscle phenotype. Methods: Eighteen Wistar rats were divided into the following 3 groups: sedentary (S); moderate‐intensity training (MIT); and high‐intensity training (HIT). The training protocol lasted 8 weeks. Forty‐eight hours after training, total RNA and protein levels in the soleus and plantaris muscles were obtained. Results: In the plantaris, the BDNF protein level was lower in the HIT than in the S group (P < 0.05). A similar effect was found in the soleus (without significant difference). In the soleus, higher Bdnf mRNA levels were found in the HIT group (P < 0.001 vs. S and MIT groups). In the plantaris muscle, similar Bdnf mRNA levels were found in all groups. Conclusions: These results indicate that high‐intensity chronic exercise reduces BDNF protein level in fast muscles and increases Bdnf mRNA levels in slow muscles. Muscle Nerve 53: 446–451, 2016     

On the role of 5‐HT1A receptor gene in behavioral effect of brain‐derived neurotrophic factor

Experiments were made on a congenic AKR.CBA‐D13Mit76C (76C) mouse strain created by transferring a chromosome 13 fragment containing the 5‐HT_1A receptor gene from a CBA strain to an AKR background. It was shown that 76C mice differed from AKR mice by decreased 5‐HT_1A receptor and tryptophan hydroxylase‐2 (tph‐2) genes expression in the midbrain. Functional activity of 5‐HT_2A receptors and 5‐HT_2A receptor mRNA levels in the midbrain and hippocampus of 76C mice were decreased compared with AKR mice. Central brain‐derived neurotrophic factor (BDNF) administration (300 ng i.c.v.) reduced 5‐HT_1A and 5‐HT_2A receptor mRNA levels in the frontal cortex and tph‐2 mRNA level in the midbrain of AKR mice. However, BDNF failed to produce any effect on the expression of 5‐HT_1A, 5‐HT_2A, and tph‐2 genes in 76C mice but decreased functional activity of 5‐HT_2A receptors in 76C mice and increased it in AKR mice. BDNF restored social deficiency in 76C mice but produced asocial behavior (aggressive attacks towards young mice) in AKR mice. The data indicate that a small genetic variation altered the response to BDNF and show an important role of 5‐HT_1A receptor gene in the 5‐HT system response to BDNF treatment and in behavioral effects of BDNF. © 2014 Wiley Periodicals, Inc.     

Electrically induced brain‐derived neurotrophic factor release from schwann cells

Regulating the production of brain‐derived neurotrophic factor (BDNF) in Schwann cells (SCs) is critical for their application in traumatic nerve injury, neurodegenerative disorders, and demyelination disease in both central and peripheral nervous systems. The present study investigated the possibility of using electrical stimulation (ES) to activate SCs to release BDNF. We found that short‐term ES was capable of promoting BDNF production from SCs, and the maximal BDNF release was achieved by ES at 6 V (3 Hz, 30 min). We further examined the involvement of intracellular calcium ions ([Ca₂₊]_i) in the ES‐induced BDNF production in SCs by pharmacological studies. We found that the ES‐induced BDNF release required calcium influx through T‐type voltage‐gated calcium channel (VGCC) and calcium mobilization from internal calcium stores, including inositol triphosphate‐sensitive stores and caffeine/ryanodine‐sensitive stores. In addition, calcium‐calmodulin dependent protein kinase IV (CaMK IV), mitogen‐activated protein kinase (MAPK), and cAMP response element‐binding protein (CREB) were found to play important roles in the ES‐induced BDNF release from SCs. In conclusion, ES is capable of activating SCs to secrete BDNF, which requires the involvement of calcium influx through T‐type VGCC and calcium mobilization from internal calcium stores. In addition, activation of CaMK IV, MAPK, and CREB were also involved in the ES‐induced BDNF release. The findings indicate that ES can improve the neurotrophic ability in SCs and raise the possibility of developing electrically stimulated SCs as a source of cell therapy for nerve injury in both peripheral and central nervous systems. © 2014 Wiley Periodicals, Inc.     

The brain‐derived neurotrophic factor Val66Met polymorphism affects encoding of object locations during active navigation

The brain‐derived neurotrophic factor (BDNF) was shown to be involved in spatial memory and spatial strategy preference. A naturally occurring single nucleotide polymorphism of the BDNF gene (Val66Met) affects activity‐dependent secretion of BDNF. The current event‐related fMRI study on preselected groups of ‘Met’ carriers and homozygotes of the ‘Val’ allele investigated the role of this polymorphism on encoding and retrieval in a virtual navigation task in 37 healthy volunteers. In each trial, participants navigated toward a target object. During encoding, three positional cues (columns) with directional cues (shadows) were available. During retrieval, the invisible target had to be replaced while either two objects without shadows (objects trial) or one object with a shadow (shadow trial) were available. The experiment consisted of blocks, informing participants of which trial type would be most likely to occur during retrieval. We observed no differences between genetic groups in task performance or time to complete the navigation tasks. The imaging results show that Met carriers compared to Val homozygotes activate the left hippocampus more during successful object location memory encoding. The observed effects were independent of non‐significant performance differences or volumetric differences in the hippocampus. These results indicate that variations of the BDNF gene affect memory encoding during spatial navigation, suggesting that lower levels of BDNF in the hippocampus results in less efficient spatial memory processing.     

Infusion of brain‐derived neurotrophic factor into the ventral tegmental area switches the substrates mediating ethanol motivation

Recent work has shown that infusion of brain‐derived neurotrophic factor (BDNF) into the ventral tegmental area (VTA) promotes a switch in the mechanisms mediating morphine motivation, from a dopamine‐independent to a dopamine‐dependent pathway. Here we showed that a single infusion of intra‐VTA BDNF also promoted a switch in the mechanisms mediating ethanol motivation, from a dopamine‐dependent to a dopamine‐independent pathway (exactly opposite to that seen with morphine). We suggest that intra‐VTA BDNF, via its actions on TrkB receptors, precipitates a switch similar to that which occurs naturally when mice transit from a drug‐naive, non‐deprived state to a drug‐deprived state. The opposite switching of the mechanisms underlying morphine and ethanol motivation by BDNF in previously non‐deprived animals is consistent with their proposed actions on VTA GABA_A receptors.     

Effects of escitalopram on the regulation of brain‐derived neurotrophic factor and nerve growth factor protein levels in a rat model of chronic stress

Escitalopram (ES‐CIT) is a widely used, highly specific antidepressant. Until now there has been very little evidence on how this drug under pathological conditions affects an important feature within the pathophysiology of stress‐related disorders such as depression: the endogenous neurotrophins. By using a well‐characterized rat model in which chronic stress induces depressive‐like behavior, the levels of neurotrophins brain‐derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were determined in representative brain regions and serum using a highly sensitive improved fluorometric two‐site ELISA system. There was a significant increase of BDNF in the left and right cortices after stress treatment (twofold increase) that was reversed by application of ES‐CIT. An ES‐CIT‐dependent NGF reduction in stressed rats was detectable in the right cortex only (P = 0.027). The left hippocampus revealed significantly higher amounts of BDNF (2.5‐fold increase) protein than the right hippocampus. These interhemispheric differences were unrelated to stress or ES‐CIT treatment in all animals. BDNF and NGF of the frontal cortex, cerebellum, and serum did not change between the study groups. There was a negative correlation between body weight and serum BDNF, independent of stress or ES‐CIT treatment. In conclusion, BDNF and NGF show substantial changes in this rodent model of chronic social stress, which is susceptible to antidepressant treatment with ES‐CIT and therefore may constitute a neurobiological correlate for the disease. © 2009 Wiley‐Liss, Inc.     

Intracerebral adult stem cells transplantation increases brain-derived neurotrophic factor levels and protects against phencyclidine-induced social deficit in mice

Stem cell-based regenerative therapy is considered a promising cellular therapeutic approach for the patients with incurable brain diseases. Mesenchymal stem cells (MSCs) represent an attractive cell source for regenerative medicine strategies for the treatment of the diseased brain. Previous studies have shown that these cells improve behavioral deficits in animal models of neurological disorders such as Parkinson''s and Huntington''s diseases. In the current study, we examined the capability of intracerebral human MSCs transplantation (medial pre-frontal cortex) to prevent the social impairment displayed by mice after withdrawal from daily phencyclidine (PCP) administration (10 mg kg⁻¹ daily for 14 days). Our results show that MSCs transplantation significantly prevented the PCP-induced social deficit, as assessed by the social preference test. In contrast, the PCP-induced social impairment was not modified by daily clozapine treatment. Tissue analysis revealed that the human MSCs survived in the mouse brain throughout the course of the experiment (23 days). Significantly increased cortical brain-derived neurotrophic factor levels were observed in the MSCs-treated group as compared with sham-operated controls. Furthermore, western blot analysis revealed that the ratio of phosphorylated Akt to Akt was significantly elevated in the MSCs-treated mice compared with the sham controls. Our results demonstrate that intracerebral transplantation of MSCs is beneficial in attenuating the social deficits induced by sub-chronic PCP administration. We suggest a novel therapeutic approach for the treatment of schizophrenia-like negative symptoms in animal models of the disorder.     

Brain‐derived neurotrophic factor: mRNA expression and protein distribution in the brain of the teleost Nothobranchius furzeri

BDNF (brain‐derived neurotrophic factor) is a member of the neurotrophin family and it is implicated in regulating brain development and function. The BDNF gene organization and coding sequence are conserved in all vertebrates. The present survey was conducted in a teleost fish, Nothobranchius furzeri, because it is an emerging model of aging studies due to its short lifespan and shows the high rate of adult neurogenesis typical of anamniotes. The present survey reports: 1) the identification and characterization of the cDNA fragment encoding BDNF protein, and 2) the localization of BDNF in the whole brain. BDNF mRNA expression was assessed by in situ hybridization, by employing an antisense RNA probe; BDNF protein was detected by employing a sensitive immunohistochemical technique, along with highly specific affinity‐purified antibodies to BDNF. Both BDNF mRNA and protein were detected in neurons and glial cells of all regions of the brain of N. furzeri. Interestingly, BDNF was localized also in brain areas involved in adult neurogenic activities, suggesting a specific role for this neurotrophic factor in controlling cell proliferation. These results provide baseline information for future studies concerning BDNF involvement in the aging processes of the teleost brain. J. Comp. Neurol. 522:1004–1030, 2014. © 2013 Wiley Periodicals, Inc.     

Intracellular calcium and calmodulin link brain‐derived neurotrophic factor to p70S6 kinase phosphorylation and dendritic protein synthesis

The mammalian target of rapamycin (mTOR)/p70S6 kinase (S6K) pathway plays an important role in brain‐derived neurotrophic factor (BDNF)‐mediated protein synthesis and neuroplasticity. Although many aspects of neuronal function are regulated by intracellular calcium ([Ca²⁺]_i) and calmodulin (CaM), their functions in BDNF‐induced phosphorylation of p70S6K and protein synthesis are largely unknown. Here, we report that BDNF, via TrkB‐dependent activation of mTOR, induces sustained phosphorylation of p70S6K at Thr389 and Thr421/Ser424. BDNF‐induced phosphorylation at Thr389 was dependent on PI3 kinase but independent of ERK‐MAPK. The previously identified MAPK phosphorylation site at Thr421/Ser424 required both PI3K and MAPK in BDNF‐stimulated neurons. Furthermore, we found that the reduction in [Ca²⁺]_i, but not extracellular calcium, blocked the BDNF‐induced phosphorylation of p70S6K at both sites. Inhibition of CaM by W13 also blocked p70S6K phosphorylation. In correlation, W13 inhibited BDNF‐induced local dendritic protein synthesis. Interestingly, sustained elevation of [Ca²⁺]_i by membrane depolarization antagonized the BDNF‐induced p70S6K phosphorylation. Finally, the BDNF‐induced p70S6K phosphorylation did not require the increase of calcium level through either extracellular influx or PLC‐mediated intracellular calcium release. Collectively, these results indicate that the basal level of intracellular calcium gates BDNF‐induced activation of p70S6K and protein synthesis through CaM. © 2009 Wiley‐Liss, Inc.     

Reduced levels of brain‐derived neurotrophic factor contribute to synaptic imbalance during the critical period of respiratory development in rats

Previously, our electrophysiological studies revealed a transient imbalance between suppressed excitation and enhanced inhibition in hypoglossal motoneurons of rats on postnatal days (P) 12–13, a critical period when abrupt neurochemical, metabolic, ventilatory and physiological changes occur in the respiratory system. The mechanism underlying the imbalance is poorly understood. We hypothesised that the imbalance was contributed by a reduced expression of brain‐derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition. We also hypothesised that exogenous BDNF would partially reverse this synaptic imbalance. Immunohistochemistry/single‐neuron optical densitometry, real‐time quantitative PCR (RT‐qPCR) and whole‐cell patch‐clamp recordings were done on hypoglossal motoneurons in brainstem slices of rats during the first three postnatal weeks. Our results indicated that: (1) the levels of BDNF and its high‐affinity tyrosine receptor kinase B (TrkB) receptor mRNAs and proteins were relatively high during the first 1–1.5 postnatal weeks, but dropped precipitously at P12–13 before rising again afterwards; (2) exogenous BDNF significantly increased the normally lowered frequency of spontaneous excitatory postsynaptic currents but decreased the normally heightened amplitude and frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) during the critical period; (3) exogenous BDNF also decreased the normally heightened frequency of miniature IPSCs at P12–13; and (4) the effect of exogenous BDNF was partially blocked by K252a, a TrkB receptor antagonist. Thus, our results are consistent with our hypothesis that BDNF and TrkB play an important role in the synaptic imbalance during the critical period. This may have significant implications for the mechanism underlying sudden infant death syndrome.     

Short‐term low‐frequency electrical stimulation enhanced remyelination of injured peripheral nerves by inducing the promyelination effect of brain‐derived neurotrophic factor on Schwann cell polarization

Electrical stimulation (ES) has been found to aid repair of nerve injuries and have been shown to increase and direct neurite outgrowth during stimulation. However, the effect of ES on peripheral remyelination after nerve damage has been investigated less well, and the mechanism underlying its action remains unclear. In the present study, the crush‐injured sciatic nerves in rats were subjected to 1 hr of continuous ES (20 Hz, 100 μsec, 3 V). Electron microscopy and nerve morphometry were performed to investigate the extent of regenerated nerve myelination. The expression profiles of P0, Par‐3, and brain‐derived neurotrophic factor (BDNF) in the injuried sciatic nerves and in the dorsal root ganglion neuron/Schwann cell cocultures were examined by Western blotting. Par‐3 localization in the sciatic nerves was determined by immunohistochemistry to demonstrate Schwann cell polarization during myelination. We reported that 20‐Hz ES increased the number of myelinated fibers and the thickness myelin sheath at 4 and 8 weeks postinjury. P0 level in the ES‐treated groups, both in vitro and in vivo, was enhanced compared with the controls. The earlier peak of Par‐3 in the ES‐treated groups indicated an earlier initiation of Schwann cell myelination. Additionally, ES significantly elevated BDNF expression in nerve tissues and in cocultures. ES on the site of nerve injury potentiates axonal regrowth and myelin maturation during peripheral nerve regeneration. Furthermore, the therapeutic actions of ES on myelination are mediated via enhanced BDNF signals, which drive the promyelination effect on Schwann cells at the onset of myelination. © 2010 Wiley‐Liss, Inc.